Although it is known that aspergillosis is caused by inhaled condidia, little is known about the precise events and interactions with the host that lead to successful survival and propagation of the fungus. During the initiation of aspergillosis, the surface of the inhaled conidia is the first fungal structure that comes in contact with the host. A. fumigatus condidia (spores) are known to be covered by a layer of hydrophobic proteinaceous fascicles called rodlets. The rodlet layer is believed to be responsible for the hydrophobic nature and the dispersibility of the spores. It has been shown that resting conidia of A. fumigatus with intact rodlet layers are killed much less effectively by human neutrophils that the swollen, rodletless hydrophobic conidia. It has been shown that hydrophilic conidia are more susceptible to neutrophil oxidative products and rabbit neutrophil cationic peptides. In addition, macrophages are also less able to kill hydrophobic spores that hydrophilic spores. We have cloned a gene responsible for the hydrophobicity of A. fumigatus conidia to study the survival of the conidia in the host tissue. PCR primers were constructed on the basis of highly conserved regions of the hydrophobin genes from three fungi were applied to A. fumigatus genomic DNA and a PCR product of 400bp fragment was isolated. The sequence of PCR product from A. fumigatus genome showed that it contained high sequence similarity with roda gene of Aspergillus nidulans. The PCR product was used for cloning the hydrophobin gene from genomic and cDNA libraries of A. fumigatus. A 4kb genomic DNA fragment and 1kb cDNA fragment were cloned and sequenced. The gene has two introns and codes a protein of 160 amino acids containing the 8 cysteines at the expected positions. The gene was designated as HYP1. HYP1 is developmentally regulated and expressed only when the culture reaches the sporulation stage. HYP1 gene was found to complement roda mutant of A. nidulans and restored rodlet layer in the fungus. This indicates that the HYP1 gene encosed the rodlet layer in A. fumigatus and that the gene is expressed in a heterologous host.